Spark plugs



July 14, 1959 P; DAVIS SPARK PLUGS Filed Oct. 8, 195

INVENTOR Dar/5 United States Patent SPARK PLUGS Putnam Davis, Larchmont,N.Y., assignor to Jet Ignition $0., Inc., Larchmont, N.Y., a corporationof New ork Application October 8, 1954, Serial No. 461,061 8 Claims.(Cl. 313- 143) this constricted passage or ignition chamber and a heador insert disposed in the end of the constricted passage opening towardthe associated cylinder having helical passages establishingcommunication between the ignition chamber and nearly axial jet passagesof smaller cross-section opening into the associated cylinder.

In a spark plug of the above described character, the combustiblemixture is propelled through the jet passages and helical passages ofthe head into the ignition chamber during the compression stroke and thehelical passages cause swirling of the mixture in the ignition chamber.It can be theorized that when a spark is made to jump across the gapbetween the electrodes, the swirling action in the ignition chamber willserve to draw the spark from a central portion of the gap toward theedge portion thereof, thereby increasing the length of the spark anddecreasing its amperage. The lengthening of the spark reduces itsheating effect on the electrodes and the danger of pitting of theelectrodes, and it also makes the ignition more effective, particularlyduring starting. The combustible mixture ignited in the ignition chamberexpands and is thereby forcibly ejected through the helical and jetpassages of the head into the cylinder to ignite the main charge in thelatter. By reason of the reduced cross-section of the jet passages, theignited mixture ejected into the cylinder is accelerated during itspassage through the jet passages to enter the cylinder at highvelocities, thereby improving the ignition of the main charge in thecylinder. Upon ignition of the main charge in the cylinder, the pressurein the cylinder becomes greater than the pressure within the body of thespark plug so that hot burnt gases start to re-enter the ignitionchamber. However, such hot burnt gases are cooled by expansion inflowing from the jet passages of relatively small cross-section into thehelical passages of larger cross-section. From the foregoing, it isapparent that heating of the electrodes from both the heat of the sparkitself and the heat of the hot burnt gases which reenter the spark plugbody is materially reduced thereby to increase the operative life of theelectrodes and, hence, of the spark plug having the above describedcharacteristics.

However, considerable difficulty has been experienced in manufacturingspark plugs having the above described characteristics, and the helicalpassages and restricted jet passages at the end of the spark plug bodyopening into the cylinder have been produced only at relatively greatexpense thereby decreasing the attractiveness of the-operativeadvantages achieved by such passages.

Accordingly, it is an object of the present invention to provide animproved construction for spark plugs of the described character wherebythe cost and difiiculty of forming the helical passages between theignition chamber of the spark plug and the communication with thecylinder and of constricting that communication are materially reduced.

A feature of this invention resides in the provision of a generallycylindrical head or insert defining the end of the ignition chamberwithin the spark plug body facing toward the cylinder and carrying oneof the electrodes, the cylindrical head having several helical groovesin the surface thereof opening radially outward and at the opposite endfaces of the head so that the helical passages are defined between saidgrooves and the adjacent inner wall surface of the spark plug body. Inorder 'to facilitate the machining of the helical groovesin the-'between a relatively large diameter portion of the interior of saidbody, in which the head is seated, and 30 the spark plug body openinginto the cylinder.

a relatively small diameter portion of the interior'of In one embodimentof the invention, the outer surface of the head or insert, at the end ofthe latter facing toward the cylinder, is bevelled to seat against theinclined shoulder on the inner wall surface of the spark plug body,whereby the ends of the helical passages adjacent the small diameterportion of the interior of the body are constricted, while in anotherembodiment of the invention the inclined shoulder is disposedimmediately adjacent the end of the head facing toward the cylinder sothat the constriction is provided between the adjacent ends of thehelical passages and the small diameter portion of the interior of thebody opening into the cylinder.

The design will give a swirling action to jet flames coming out of theplug. Such swirling jets of flame increase the turbulence of the gas-airmixture in the cylinder of the engine and assure better mixture of thegas and air and more complete and rapid combustion.

As a result of the low pressure area in the vortex created by theswirling gas-air mixture entering the combustion chamber of the plug onthe compression stroke there is less resistance (pressure) in thevortex, where the spark travels, than would be the case if the pressurewere equal throughout the entire combustion chamber. There is thereforea lower compression ratio in the vortex than there is throughout thebalance of the combustion chamber of the plug and cylinder of theengine.

The degree of taper and direction of taper of the holes or grooves makepossible the control of the heat range of the plug other than by theconventional method now employed of increasing or decreasing the lengthof the nose of the ceramic to decrease or increase the rate of heatdissipation. i

The above, and other objects, features and advantages t of the inventionwill be apparent in the following detailed description of illustrativeembodiments thereof which is to be read in connection with theaccompanying drawing forming a part hereof, and wherein:

Fig. l is an elevational view of a spark plug embodying this invention,with the spark plug body being broken away and shown in section;

Fig. 2 is a transverse section taken along the line 2-2 of Fig. l, buton an enlarged scale;

Fig. 3 is a transverse section taken along the line 3-3 of Fig. l, buton an enlarged scale;

Fig; 4 is a perspective view of an element included in the spark plug ofFigs. 1, 2 and 3;

Fig. 5 is a fragmentary elevational view of a spark plug constructed inaccordance with another embodiment of this invention, and with the sparkplug body broken away and shown in section;

Fig. 6 is a transverse section taken along the line 6-6 of Fig. 5;

Fig. 7 is a perspective view of an element included in the spark plug ofFigs. 5 and 6; and

Fig. 8 is a fragmentary elevational view of another form of insert.

Referring to the drawing in detail, and initially to Fig. 1 thereof, thespark plug embodying this invention and generally identified by thereference numeral 10 is there shown to include an insulator 11, ofconventional construction, and a hollow metal body 12. The body 12defines an interior space or passage 13 which tapers toward the lowerend of the body and communicates with a cylindrical space 14 forming anignition chamber. The insulator 11 extends into the body 12 from aboveand is held in position by a jam nut 15, with a suitable seal, forexample, a gasket 16 being provided between the insulator 11 and theside wall surface of the tapering space 13.

At its lower end, the insulator 11 carries a first electrode 17 disposedin the ignition chamber 14, and a second electrode 18 extends upwardlyfrom an insert or head 19 toward the electrode 17 in axial alignmentwith the latter.

As is usual, the lower portion of body 12 is externally threaded, as at20, for engagement in a suitably tapped hole or opening in the cylinderhead (not shown).

In accordance with this invention, the body or insert 19 issubstantially cylindrical and is formed with several helical grooves 21in the side surface thereof and opening radially and at the opposite endfaces of the insert 19. Each of the grooves 21 has a constant depthalong the length thereof with respect to the axis of the insert 19 andhas an arcuate cross-section of the same curvature along its entirelength so that the machining of the grooves can be easily andinexpensively accomplished.

As seen in Fig. l, the cylindrical space or chamber 14 of the body 12,into which the insert 19 is pressed or otherwise secured, is bounded atits lower end by an inwardly inclined shoulder 22 which separates thespace 14 from a passage 23 of relatively small diameter opening at thelower end of the spark plug body, and hence, into the cylinder.

In the embodiment of the invention illustrated in Figs. 1 to 4,inclusive, the side wall surface of the insert or head 19 is tapered orbevelled at the lower end, as at 24 (Figs. 1 and 4), and at the sameangle as the inclined shoulder 22, so that the bevelled end 24 of theinsert 19 in the space 14 seats upon the shoulder 22.

It is apparent that helical passages, communicating at their upper endswith the ignition chamber and at their lower ends with the passage 23opening into the cylinder, are defined between the helical grooves 21and the internal surface of the body 12 confronting the grooves.Sincethe upper portions of the grooves 21 are confronted by thecylindrical internal wall surface of the space 14, while the lowerportions of the grooves are confronted by the inclined shoulder 22, itis apparent that the upper portions of the helical passages haverelatively large cross-sectional areas (Fig. 3) and that the lowerportions of the helical passages are constricted or have relativelysmall cross-sectional areas (Fig. 2), these varying crosssectional areasbeing achieved with helical grooves having the same cross-sectionalcurvature and depth with respect to the axis of the insert 19 along thelengths thereof for ease in machining.

The operation of the above described spark plug 10 is as follows:

During the compression stroke of the piston in the associated cylinder,the combustible mixture enters the spark plug body 12 through thepassage 23 and then travels through the helical passages, definedbetween grooves 21 and the confronting internal wall surface of thebody, into the ignition chamber 14. The helical passages impart aswirling motion to the combustible mixture entering the ignitionchamber. On ignition, the voltage applied to electrode 17 causes a sparkto jump across the center of the gap between the electrodes 17 and 18.In one aspect, it can be theorized that the swirling motion of themixture in the ignition chamber serves to draw the spark away from thecenter of the gap to the edge portion of the latter, thereby increasingthe length of the spark and correspondingly decreasing its amperage. Thelengthening of the spark in the above manner tends to reduce the extentto which it heats the electrodes and the danger of pitting of theelectrodes, and the lengthened spark also improves the effectiveness ofthe ignition, particularly during starting.

Following ignition of the mixture in chamber 14, the ignited mixtureexpands and is thereby forcibly ejected through the helical passages andthe passage 23 into the cylinder to ignite the main charge in thelatter. Since the helical passages are constricted at the lower portionsof the grooves 21 by reason of the inclined shoulder 22, the ignitedmixture ejected into the passage 23 is accelerated and enters thecylinder at a high velocity thereby to improve the ignition of the maincharge.

When the main charge in the cylinder is ignited, the pressure in thecylinder becomes greater than that in the body of the spark plug so thathot burnt gases start to re-enter the spark plug body through thepassage 23 and the helical passages extending from the latter to thechamber 14. However, since the helical passages have smallercrosssectional areas at their lower ends than along their upperportions, the hot burnt gases expand during their travel through thehelical passages and are thereby cooled before entering the chamber 14containing the electrodes. Thus, the heating of the electrodes by thehot burnt gases is held to a minimum.

In the embodiment of the invention illustrated in Figs. 5, 6 and 7, theseveral parts of the spark plug are identified by the same referencenumerals employed in connection with the corresponding parts of theembodiment of Figs. 1 to 4, inclusive, but with the letter a annexedthereto. Thus, the spark plug 10a includes an insulator 11a extendinginto the ignition chamber 14a defined within the metal body 12a, and theaxially aligned and spaced apart electrodes 17a and 18:: arerespectively carried by the insulator 11a and an insert or head 1%disposed in the ignition chamber.

As in the first described embodiment, the insert 19a is formed withseveral helical grooves 21a in the side wall surface thereof openingradially and at the opposite end faces of the insert, the grooves 21abeing at the same depth with respect to the axis of the insert andhaving the same cross-sectional curvatures along their entire lengthsfor each in machining. As distinguished from the insert 19, the insert19a (Figs. 5 and 7) is cylindrical along its entire length, with theexception of the grooves 21a, so that the lower edge of the insert 19ais held above the inclined shoulder 22a. Accordingly, the helicalpassages defined between the grooves 21a and the internal wall surfaceof body 12a, which is cylindrical throughout the length of the insert19a, are of the same cross-sectional -area along their entire lengths.However, the inclined shoulder 22a confronts or extends partly acrossthe lower ends of the helical passages to provlde a constriction betweenthe latter and the relatively small diameter passage 23a opening intothe cylinder. Thus, following ignition of a combustible mixture inchamber 14a, the ignited mixture passes through the heheal passages andis accelerated upon discharge from the latter into passage 23a past theshoulder 22a, thereby to enter the cylinder at high velocity. Further,after ignition of the main change in the cylinder, any hot burnt gasesre- .entering the body 12a are expanded and correspondingly cooledduring passage by the shoulder 22a before entering the helical passages.From the foregoing, it is apparent that the spark plug a has the sameoperative advantages as the plug 10 although the constriction at theends of the helical passages opening toward the cylinder is effected ina different manner.

Another form is illustrated in Fig. 8, wherein body 12 has insert 25with tangentially drilled holes 26, the flames from said holes strikingthe interior of the body 12 or wall 27 to produce a swirling action. Theholes 26 may be tapered in either direction.

Although specific illustrative embodiments of the invention have beendescribed in detail herein and shown in the accompanying drawing, it isto be understood that the invention is not limited to these preciseembodiments and that various changes and modifications may be effectedtherein without departing from the scope or spirit of the invention, asdefined in the appended claims.

What is claimed is:

1. A spark plug comprising a hollow body having a cylindrical internalspace defining an ignition chamber and a smaller diameter passageopening at the adjacent end of the body, with an annular inclinedshoulder between said cylindrical internal space and smaller diameterpassage, two axially aligned and spaced apart electrodes in saidignition chamber, and a substantially cylindrical insert in saidcylindrical internal space at the end of the latter adjacent saidpassage, said insert having its lower external wall inclined inwardly soas to seat on said annular inclined shoulder, said insert having helicalgrooves in the side wall surface opening radially and at the oppositeend faces of the insert so that helical passages are defined betweensaid grooves and the internal wall surface of said body to communicatesaid ignition chamber with said small diameter passage while saidinclined shoulder defines a constriction adjacent the ends of saidhelical passages opening towards said small diameter passage.

2. A spark plug comprising a hollow body having a cylindrical internalspace defining an ignition chamber and a smaller diameter passageopening at the adjacent end of the body, with an annular inclinedshoulder between said cylindrical internal space and smaller diameterpassage, two axially aligned and spaced apart electrodes in saidignition chamber, and a substantially cylindrical insert in saidcylindrical internal space at the end of the latter adjacent saidpassage, said insert having its lower external wall inclined inwardly soas to seat on said annular inclined shoulder, said insert having helicalgrooves in the side Wall surface opening radially and at the oppositeend faces of the insert, said grooves being of the same depth withrespect to the axis of said insert and having the same cross-sectionalcurvature along the lengths thereof, said grooves and the confrontinginternal wall surface of the body defining helical passagescommunicating said ignition chamber with said small diameter passagewhile said inclined shoulder defines a constriction adjacent the ends ofsaid helical passages opening towards said small diameter passage.

3. A spark plug comprising a hollow body having a cylindrical internalspace defining an ignition chamber and a smaller diameter passageopening at the adjacent end of the body, with an annular inclinedshoulder between's'aid cylindrical internal space and smaller diameterpassage, two axially aligned and spaced apart electrodes in saidignition chamber, and a substantially cylindrical insert in saidcylindrical internal space at the end of the latter adjacent saidpassage, said insert having its lower external wall inclined inwardly soas to seat on said annular inclined shoulder, said insert having helicalgrooves in the side wall surface opening radially and at the oppositeend faces of the insert, said grooves being of the same depth withrespect to the axis of said insert and having the same cross-sectionalcurvature along the lengths thereof, the end of said insert facingtoward said small diameter passage being bevelled and seating againstsaid inclined shoulder so that helical passages are defined between saidgrooves and the confronting internal wall surface of said body with thecross-sectional areas of said helical passages at the ends opening intosaid ignition chamber being larger than the cross-sectional areasthereof at the ends opening into said small diameter passage.

4. A spark plug comprising a hollow body having a cylindrical internalspace defining an ignition chamber and a smaller diameter passageopening at the adjacent end of the body, with an annular inclinedshoulder between said cylindrical internal space and smaller diameterpassage, two axially aligned and spaced apart electrodes in saidignition chamber, and a substantially cylindrical insert in saidcylindrical internal space at the end of the latter adjacent saidpassage, said insert having its lower external wall inclined inwardly soas to seat on said annular inclined shoulder, said insert having helicalgrooves in the side wall surface opening radially and at the oppositeend faces of the insert, said grooves having the same cross-sectionalareas along the lengths thereof and the portions of said insert betweensaid grooves having the same radius as said cylindrical internal spacethroughout the length of said insert, said insert being arranged in saidcylindrical internal space with an end face of the insert contiguouswith the large diameter end of said inclined shoulder, said grooves andthe confronting internal wall surface of said body defining helicalpassages between said ignition chamber and said smaller diameter passagewith said inclined shoulder forming a constriction adjacent the ends ofsaid helical passages opening into said smaller diameter passage.

5. A spark plug comprising a hollow body having a stepped interioropening axially at the relatively small diameter portion thereof forcommunication with a cylinder and with an inclined shoulder between saidrelatively small diameter portion and the relatively large diameterportion of said stepped interior, an insulator extending into said largediameter portion of the interior through the end of the latter remotefrom said shoulder and carrying a first electrode, and an insert in saidlarge diameter portion of the interior against said shoulder andcarrying a second electrode axially aligned and spaced apart withrespect to said first electrode, said insert having its lower externalwall inclined inwardly so as to seat on said annular inclined shoulder,said insert having at least one helical groove in the periphery thereofopening radially outward and at the opposite end faces of the insert,each of said grooves and the confronting internal surface of said bodydefining a helical passage communicating the space around saidelectrodes with said small diameter portion of the interior while saidinclined shoulder defines a constriction adjacent the end of saidhelical passage opening into said small diameter portion of theinterior.

6. A spark plug according to claim 5; wherein each groove of the inserthas the same depth with respect to the axis of the insert and the samecross-sectional curvature along its entire length.

7. A spark plug according to claim 6; wherein the end of said insertadjacent said small diameter portion of the interior has a bevelled edgeseating face-to face against said inclined shoulder so that the portionof said has a smaller cross-sectional area than the remainder of saidhelical passage.

8. A spark plug according to claim 6; wherein said insert has the samecross-sectional configuration throughout its length and is Whollycontained in said large diameter portion of the interior so that saidhelical'passaige has the same cross-sectional area throughout its lengthand the constriction defined by said inclined shoulder isdisposedbetween said small diameter portion of the interior and the adjacent endof said helical passage.

References Cited in the file ofthis patent UNITED STATES PATENTS SpencerApr. 4, 1911 Gottlieb Apr. 12, 1921 Gavlak Oct. 13, 1925 Powell Sept.23, 1930 Harper Aug. 23, 1938 Harper June 18, 1940 FOREIGN PATENTSFrance Nov. 18, 1953

